There has been an internal combustion engine that includes an intake passage injector for injecting fuel into an intake passage of an internal combustion engine and an in-cylinder injector for injecting the fuel into a combustion chamber of the internal combustion engine, and determines a fuel injection ratio between the intake passage injector and the in-cylinder injector based on a revolution speed of the internal combustion engine and a load of the internal combustion engine.
The in-cylinder injector is exposed to a hot combustion gas in a combustion chamber so that deposits are liable to adhere onto a nozzle unit of the in-cylinder injector. Further, when the fuel is injected only from the intake passage injector, the in-cylinder injector does not inject the fuel so that cooling by vaporization of the fuel does not occur, and the temperature of the nozzle unit rises, resulting in further production of the deposits on the nozzle unit. These deposits interfere with the fuel injection from the nozzle unit, and change a form of a fuel spray to increase a particle diameter. Also, a quantity of the injected fuel becomes smaller than a required quantity, which may cause misfire and thus a combustion failure.
Japanese Patent Laying-Open No. 2005-201083 has disclosed an injection control device of an internal combustion engine that can appropriately suppress production of deposits on a nozzle unit of an in-cylinder injector. This injection control device of the internal combustion engine includes an in-cylinder injector injecting fuel into a cylinder of the internal combustion engine, an intake passage injector injecting the fuel into an intake passage and a control unit that controls driving of at least one of these injectors to change a form of the fuel injection. The control unit forcedly changes the fuel injection form to inject the fuel only by the in-cylinder injector for a predetermined period when the engine is in a drive region where the intake passage injector injects the fuel.
Since this fuel injection control device of the internal combustion engine is configured to perform the fuel injection only by the in-cylinder injector for the predetermined period even when the engine is in the region where the fuel injection is to be performed only by the intake passage injector, an injection force can blow off deposits produced on the nozzle unit of the in-cylinder injector and thus can remove the deposits. Further, the above fuel injection by the in-cylinder injector can cool the nozzle unit by vaporization of the fuel, and thereby can suppress the production of new deposits on the nozzle. Consequently, it is possible to suppress lowering of the fuel injection quantity of the in-cylinder injector.
Variations within an allowed range are present in the properties (including a state) of the fuel used in the internal combustion engine. For example, the fuel properties may be classified as being light or being heavy. When the fuel contains a large amount of olefin (unsaturated hydrocarbon with at least one carbon-carbon double bond) ingredient, the fuel is light in property. When the fuel contains a small amount of olefin ingredient, the fuel is heavy in property. When the fuel contains a large amount of olefin ingredient, there is a tendency to produce rapidly the deposits. However, Japanese Patent Laying-Open No. 2005-201083 described above has not referred to this difference in fuel property.